A bicycle derailleur hitherto disclosed in Japanese Patent Publication Gazette No. Sho 54-18,016 is so constructed that a control wire is operable even with a resistance against speed change, when a driving chain in engagement with a sprocket of a multistage sprocket assembly being stationary;is larger than that when the chain normally travels. In this device, the operating force of the control wire is energy-conserved, and when the larger resistance is released, the chain is automatically shifted to a desired sprocket by the conserved energy.
The conventional derailleur uses first and second saver arms supported swingably at both sides of one linkage member at the linkage mechanism. In this device, between each arm and the linkage mechanism are provided saver springs, and an operating arm having projections engageable with the opposite inner surfaces of the saver arms is pivoted to the linkage member. Also the control wire is fixed to the free end of the operating arm and pulled to turn the first saver arm forwardly to energy-conserve the pulling force and pushed to turn the second saver arm backwardly to energy-conserve the pushing force, thereby enabling the driving chain to be shifted by the conserved energy from the top side to the low side and vice versa.
The conventional derailleur, however, uses the two saver arms, saver springs and operating arm to energy-conserve a pulling and pushing forces, thereby creating the problem in that not only the required number of parts is resulting in a complicated construction but also the assembly procedure is troublesome, thus leading to a high manufacturing cost as a whole.